The present invention relates to a fire screening glazing panel comprising at least one layer of intumescent material sandwiched between flat vitreous sheets.
In the construction of buildings, glazing panels have often to be used in exterior or interior walls or partitions. An obvious example is the use of transparent glazing panels used in windows. Opaque glazing panels are also often used in the lower part of interior partitions.
There is an increasing requirement that such glazing panels should satisfy certain stringent standards of fire resistance. There are various modern standards in use, but broadly they lay down that when one face of such a panel is exposed to a specified heating schedule simulating a fire, the mean temperature of the other face should remain below a specified value for a specified period of time, and during the same period, the maximum temperature of any part of that face should not rise above a certain level.
Furthermore it is clearly desirable that such a panel should retain its integrity for as long as possible after the outbreak of fire so that it can remain as an effective flame and fume barrier and provide a shield against radiant heat.
One test is laid down in International Standard ISO 834 (Fire resistance tests - Elements of building construction). Briefly stated this test involves mounting the panel to be tested in the wall of a furnace which is then heated according to a predetermined schedule, and measuring the time after which the panel no longer remains intact as a flame and fume proof barrier or after which its outer face becomes unacceptably hot. Not only should the panel be resistant to thermal shock, but it should also be resistant to physical shock for as long as is practically desirable after the outbreak of fire lest a person who accidentally (or even deliberately) breaks it becomes suddenly engulfed in flame.
Various proposals have been made for the manufacture of fire screening glazing panels including in particular British Pat. No. 1,290,699 (BASF). This document teaches the use of one intumescent layer sandwiched between two glass sheets and two intumescent layers sandwiched between three sheets of glass in the manufacture of fire screening glazing panels which can be made to satisfy criteria laid down in various standards pertaining to the fire resistance of glazings.
The panels specifically proposed in the BASF specification referred to above make use of glass sheets about 3 mm in thickness and this is typical of prior proposals in the field of fire screening glazing panels.
Known fire screening panels can be made to satisfy ISO 834 for periods of up to 20 minutes without especial difficulty and longer periods of fire resistance can be achieved by taking certain additional steps.
One way is to increase the thickness of the panel. Since it is well known in the art thick vitreous sheets are more apt to crack due to thermal shock to which they would inevitably be subjected on the outbreak of fire, the maximum individual sheet thickness envisaged in prior art proposals has been 5 mm, and further increases in panel thickness have been achieved by using additional sheets and layers of intumescent material. This adds considerably to costs and manufacturing difficulties.
A second way is to mount two known fire screening panels in a double panel frame, but such double panels are again expensive and are rather too cumbersome for use in some circumstances.
A third way is to include glass fibres and wire mesh in an intumescent layer, but this also gives rise to manufacturing difficulties and, in the case of transparent fire screening glazing panels, with which this invention is particularly but not exclusively concerned, the addition of such materials detracts from the appearance and light transmissivity of the panel.